This is the act and enjoyment of applying whipped cream in and around a woman's vagina who is on her period. Then proceeding to eat her out. A dessert and delight for the sickest of fucks.
Guy 1: "Dude, it sucks, my girlfriend got her period."
Guy 2: "No that's awesome. Now you can have a Sundae Bloody Sundae."
A variation on the chocolate sundae in which someone shits on another person's chest, ejaculates on top of it, then smears it around the person's chest and genitalia.
"Yeah, she's into some really weird shit... Last night I gave her a sundae musher and she spooned it off and ate the whole damn thing."